T cell activation is an important step in the protective immunity against pathogenic microorganisms (e.g., viruses, bacteria, and parasites), foreign proteins, and harmful chemicals in the environment, and also as immunity against cancer and other hyperproliferative diseases. T cells express receptors on their surfaces (i.e., T cell receptors) that recognize antigens presented on the surface of cells. During a normal immune response, binding of these antigens to the T cell receptor, in the context of MHC antigen presentation, initiates intracellular changes leading to T cell activation.
Adoptive T cell therapy has been used to treat hyperproliferative diseases, including tumors, by providing an antigen-specific immune response. One method involves the use of genetically modified T cells that express an antigen-specific protein having an extracellular domain that binds to an antigen.